A standard deviation of greater than 4.48 degrees would make 8.6 degrees above average insignificant, assuming a normal distribution (alpha = 0.05, two-sided Z-test).
I do understand what standard deviation is, and I do understand that it is possible that a 8.6 degrees difference would be significant. What I meant was that NOAA wouldn't be highlighting this unless it was.
Anyway, it's public data, and we can settle this pretty easily, right?
http://www.ncdc.noaa.gov/temp-and-precip/time-series/index.p... has the raw data in CSV form going back to 1895.
The standard deviation is 2.89 (assuming my calculations are correct)